Certain types of fish are considered to be risky foods for nursing mothers, infants, and young children because of high levels of mercury, a heavy metal that can damage developing brains and nervous systems. But a new study shows that rice cereal—a food that’s far more likely to be included in childrens' diets than big-eye tuna or swordfish—can also be a potential source of mercury.

Writing in the Journal of Agricultural and Food Chemistry, a team of researchers led by scientists from Florida International University found that rice-based cereals—which are often the first food given to infants—contained significantly higher levels of mercury than those made with other grains.

The team purchased 119 common brands of rice, multigrain, and non-rice cereals from local grocery stores and online. About half of the cereals studied came from four large cities across the U.S. (Miami, New York City, San Jose, and Chicago) and the other half from four cities in China (Beijing, Wuhan, Nanjing, and Qingdao). The researchers then measured how much mercury was present in each of the cereals, and estimated how much was getting into infants’ bodies each day after eating them. 

The results showed that rice cereals had on average three times the amount of methylmercury, the most concerning type, as multigrain cereals, and 19 times the amount in cereals made with grains other than rice. Other research has shown that rice plants pick up more methylmercury from their environment than other grain plants. There were no major differences in mercury levels between cereals purchased in China and the U.S., nor between major brands, the researchers reported.  

A Growing Concern

Excess mercury can be harmful to adults too, causing loss of peripheral vision, "pins and needles" feelings in the hands, feet, and mouth, uncoordinated movements, muscle weakness, and impaired speech and hearing. In 2001, the Environmental Protection Agency (EPA) set a limit for how much mercury everyone can safely be exposed to before it’s likely to cause problems, but health experts have cautioned that these levels may need to be re-evaluated for babies and young children.

“For infants, we typically think of mercury coming from breast milk, but this study shows that there are other sources we haven’t considered,” says Yong Cai, Ph.D., chair of the Department of Chemistry and faculty member of the Biochemistry and the Southeast Environmental Research Center at Florida International University. He’s also one of the co-authors of the study.

What Parents Can Do

According to Cai, parents shouldn’t panic. The majority of rice cereal samples tested were below the EPA’s limit. But he says the results of this study suggest that public health experts, scientists, and parents need to pay more attention to unexpected sources of mercury in childrens’ diets. 

Limiting rice cereals appears to be a good first step and may also minimize a child’s exposure to other heavy metals. In 2014, CR testing found that infant rice cereals often contain worrisome amounts of arsenic, another heavy metal.

“Arsenic in rice has previously raised a lot of concern, and this new mercury finding is yet another good reason you shouldn’t feed your baby too much rice cereal,” says Jean Halloran, director of Food Policy Initiatives at Consumers Union, the policy and mobilization arm of Consumer Reports. “Not only does it contain arsenic which can cause cancer, but it contains mercury, which can cause brain damage.”

CR recommends that babies have no more than ¼ cup of rice cereal a day, assuming that is the only rice product they consume. The Food and Drug Administration suggests that you should avoid feeding your child rice and rice products as their first food, and instead incorporate a variety of iron-fortified cereals made with other grains such as oats or barley.